1. Field of the Invention
The present invention relates to semiconductor modules used in power conversion devices such as inverters and converters, and particularly to the arrangement of semiconductor devices in the module.
2. Description of the Background Art
The semiconductor modules used in power conversion devices such as inverters and converters include MOSFET modules containing a plurality of MOSFET (Metal Oxide Semiconductor Field Effect Transistor) devices, diode modules containing a plurality of diode devices, and IGBT modules containing a plurality of IGBT (Insulated Gate Bipolar Transistor) devices and diode devices, for example. IGBT modules containing a plurality of semiconductor devices, IGBT devices and diode devices, connected in parallel will be described herein as an example of the semiconductor module.
The conventional IGBT modules include that described in xe2x80x9cA Novel Low-Cost and High-Reliability IGBT Module for General Use,xe2x80x9d written by E.Tamba, M.Sasaki, S.Sekine, Y.Sonobe, K.Suzuki, K.Yamada, R.Saito, T.Terasaki, O.Suzuki, T.Shigemura et al. European Conference on Power Electronics and Applications 1997, Trondheim, for example. FIG. 8 is a plane view mainly showing the semiconductor device area in this conventional IGBT module and FIG. 9 is a sectional view mainly showing an area including an IGBT device and a diode device in the module.
In FIGS. 8 and 9, the conventional semiconductor module includes a radiation board 1 made of metal, e.g. copper, for cooling the semiconductor devices, insulating substrates 2 made of aluminum nitride or the like and bonded on the radiation board 1, electrode patterns 2a bonded on both sides of the insulating substrates 2, and IGBT devices 3 and diode devices 4 as semiconductor devices bonded on the metal patterns 2a on the insulating substrates 2. Each IGBT device 3 has an emitter electrode 5 and a gate electrode 6 formed on its one side and a collector electrode 7 formed on the entire surface on the other side, and each diode device 4 has an anode electrode 8 formed on its one side and a cathode electrode 9 formed on the entire surface on the other side thereof. Emitter relay substrates 10, collector relay substrates 11, and gate interconnection substrates 12 are bonded on the radiation board 1, and electrode patterns 10a, 11a, and 12a are respectively bonded on both sides of the substrates.
It also includes aluminum wires 13a, 13b, 13c as interconnections, a module emitter electrode 14, a module collector electrode 15, and module gate electrodes 16 as external terminals, a case 17 made of a resin material and fixed on the radiation board 1, and resin 18 sealing the inside of the case 17.
As shown in FIGS. 8 and 9, the insulating substrates 2 are bonded with solder on the radiation board 1 and the IGBT devices 3 and the diode devices 4 are bonded side by side with solder on the electrode patterns 2a on the insulating substrates 2. Each emitter electrode 5 on the surface of the IGBT device 3 and the anode electrode 8 on the surface of the diode device 4 are connected through the aluminum wires 13a, which are further connected to the electrode pattern 10a on the emitter relay substrate 10.
The electrode pattern 2a on the insulating substrate 2, to which the IGBT device 3 and the diode device 4 are bonded, is connected to the electrode pattern 11a on the collector relay substrate 11 through the aluminum wires 13b, so as to connect the collector electrode 7 on the back of the IGBT device 3, the cathode electrode 9 on the back of the diode device 4, and the electrode pattern 11a on the collector relay substrate 11.
In this way, this semiconductor module contains four IGBT devices 3 and four diode devices 4, where the IGBT devices 3 and the diode devices 4 are connected in inverse parallel. That is to say, the devices are connected to form one module in such a manner that the emitter electrode 5 of the IGBT device 3 and the anode electrode 8 of the diode device 4 are at the same potential and the collector electrode 7 of the IGBT device 3 and the cathode electrode 9 of the diode device 4 are at the same potential.
The module emitter electrode 14 as an external emitter terminal is connected to the electrode patterns 10a on the emitter relay substrates 10, and the module collector electrode 15 as an external collector terminal is connected to the electrode patterns 11a on the collector relay substrates 11. These external terminals 14 and 15 make connections to other semiconductor modules and the like (not shown) outside the case 17 to form a circuit like an inverter. The gate electrode 6 of each IGBT device 3 is connected to the electrode pattern 12a on the gate interconnection substrate 12 through the aluminum wire 13c to control the gate potential for turning on/off the IGBT device 3, and the electrode pattern 12a is further connected to the module gate electrode 16 serving as an external gate terminal.
FIG. 10 shows a circuit diagram of a three-phase inverter circuit as a typical example of a circuit to which the IGBT module is applied. FIG. 10 shows IGBT modules 19 on the positive side, IGBT modules 20 on the negative side, a positive terminal 21 of DC voltage source, a negative terminal 22 of DC voltage source, a collector terminal 23 of the positive-side IGBT module 19 in the U phase, and an emitter terminal 24 of the negative-side IGBT module 20. The connection point 25 between the emitter terminal of the positive-side IGBT module 19 and the collector terminal of the negative-side IGBT module 20 is a U-phase output terminal.
The power conversion devices like inverters using the semiconductor modules are used as motor driving power source in trains, for example, which are usually installed in limited space. Therefore size reduction is extremely important.
In the conventional IGBT module constructed as described above, the semiconductor devices in the IGBT module, or the IGBT device 3 and the diode device 4, are provided side by side in the lateral direction on the radiation board 1 with the insulating substrate 2 therebetween so that the heat generated in operation can be conducted to the radiation board 1 for cooling. The emitter electrode 5 and the anode electrode 8 formed on the surfaces of the devices 3 and 4 are connected by wire bonding through the aluminum wires 13a. 
Accordingly, the area reduction of the IGBT module in the plane direction (the direction in which the semiconductor devices 3 and 4 are arranged) is limited, which hinders effective size reduction of the IGBT module.
According to a first aspect of the present invention, a semiconductor module comprises: a first semiconductor device; a second semiconductor device; and a case for accommodating the first and second semiconductor devices, wherein the first and second semiconductor devices have their respective main electrodes, and the first and second semiconductor devices are stacked, with an element connecting conductor interposed between the main electrodes.
Preferably, according to a second aspect, in the semiconductor module, the first and second semiconductor devices are stacked, with their respective main electrodes facing each other.
Preferably, according to a third aspect, in the semiconductor module, the first and second semiconductor devices are the same kind of semiconductor devices.
Preferably, according to a fourth aspect, in the semiconductor module, the main electrodes of the first and second semiconductor devices are main electrodes having the same function.
Preferably, according to a fifth aspect, in the semiconductor module, the main electrodes of the first and second semiconductor devices are main electrodes having opposite functions.
Preferably, according to a sixth aspect, in the semiconductor module, the first semiconductor device is an IGBT device, the second semiconductor device is a diode device, the semiconductor module further comprises a radiation board on which the IGBT device is provided, and the diode device is provided right above the IGBT device.
Preferably, according to a seventh aspect, in the semiconductor module, the first and second semiconductor devices and the element connecting conductor are bonded together with a conductive resin.
Preferably, according to an eighth aspect, the semiconductor module further comprises a pressurizing mechanism for pressurizing the first and second semiconductor devices from outside in directions in which the main electrodes of the first and second semiconductor devices face each other, and the first and second semiconductor devices are joined together by pressure connection with the element connecting conductor interposed therebetween.
Preferably, according to a ninth aspect, in the semiconductor module, the case comprises two conductive radiation boards, the first and second semiconductor devices stacked with the element connecting conductor interposed therebetween are provided between the two conductive radiation boards, and the pressurizing mechanism pressurizes the two conductive radiation boards in the facing directions.
As stated above, according to the semiconductor module of the first aspect of the present invention, the first semiconductor device and the second semiconductor device are stacked and connected through an element connecting conductor and accommodated in a case. This reduces the area of the semiconductor module and effectively achieves size reduction.
According to the semiconductor module of the second aspect of the invention, the first and second semiconductor devices are stacked with their respective main electrodes facing each other. This improves the cooling performance of the semiconductor module.
According to the semiconductor module of the third aspect of the invention, the first and second semiconductor devices are the same kind of semiconductor devices. This reduces the area of the semiconductor module by half and achieves further size reduction.
According to the semiconductor module of the fourth aspect of the invention, the respective main electrodes of the first and second semiconductor devices are main electrodes having the same function. Then the electric characteristics of the first semiconductor device and the second semiconductor device can be uniform and stable.
According to the semiconductor module of the fifth aspect of the invention, the respective main electrodes of the first and second semiconductor devices are main electrodes having opposite functions. This effectively achieves the size reduction of the semiconductor module in which semiconductor devices of the same kind are connected in parallel.
According to the semiconductor module of the sixth aspect of the invention, an IGBT device is provided on a radiation board and a diode device is provided right above the IGBT device. This provides a semiconductor module having excellent cooling performance.
According to the semiconductor module of the seventh aspect of the invention, the first and second semiconductor devices and the element connecting conductor are bonded together by a conductive resin. The semiconductor devices can be bonded to the element connecting conductor reliably and easily, which facilitates the process of assembling the semiconductor module.
According to the semiconductor module of the eighth aspect of the invention, the first and second semiconductor devices are joined together by pressure connection with the element connecting conductor interposed therebetween. Thus the semiconductor devices can be easily joined to the element connecting conductor, which simplifies the process of manufacturing the semiconductor module.
According to the semiconductor module of the ninth aspect of the invention, the case has two conductive radiation boards and first and second semiconductor devices stacked with the element connecting conductor interposed therebetween are provided between the two conductive radiation boards. The two conductive radiation boards are pressurized by the pressurizing mechanism in the facing directions. This allows easy and simple manufacture of an effectively downsized semiconductor module having excellent cooling performance.
The present invention has been made to solve the problems above, and an object of the present invention is to provide a module structure which can effectively promote size reduction of a semiconductor module containing a plurality of semiconductor devices connected to realize large-power switching.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.